Pump

ABSTRACT

A pump assembly including a gerotor pump having an inlet and an outlet, and comprising an annulus and a lobed rotor, one, but not both, of the rotor or annulus being split axially into two parts, the pump further comprising indexing means for angularly shifting one part relative to the other part, the indexing means comprising a chamber having a first indexing port and a second indexing port, and a partition which divides the chamber into a first portion including the first indexing port and a second portion including the second indexing port, wherein the partition comprises a part which is pivotally mounted within the chamber for angular movement within the chamber.

The present invention relates to a pump, in particular to a variable output internal gerotor pump.

Variable output internal gerotor pumps comprising an internally lobed annulus and a male lobed rotor in which one, but not both, of the annulus or rotor are split axially into two parts, and in which indexing means are provided for angularly shifting one part relative to the other, are known, for example from GB 2313411 and EP0565340A. Such angular shifting of one part relative to the other alters output flow rate of the pump.

In such known pumps, angular shifting of one part relative to the other is achieved by means of a rack or worm and pinion arrangement. In the pump disclosed in EP0565340A, a rack is provided on a piston rod of a piston provided in a cylinder connected to a source of pressurised fluid, such as the pump output. Thus, the relative angular orientation of the two parts can be achieved by varying the pressure of fluid supplied to the cylinder. Such rack/worm and pinion arrangements can, however, be bulky and the inherently elongate nature of the rack or worm can make the pump difficult to package, particularly in an automotive engine compartment where space is restricted.

According to a first aspect of the invention we provide a pump assembly including a gerotor pump having an inlet and an outlet, and comprising an annulus and a lobed rotor, one, but not both, of the rotor or annulus being split axially into two parts, the pump further comprising indexing means for angularly shifting one part relative to the other part, the indexing means comprising a chamber having a first indexing port and a second indexing port, and a partition which divides the chamber into a first portion including the first indexing port and a second portion including the second indexing port, wherein the partition comprises a part which is pivotally mounted within the chamber for angular movement between a first orientation and a second orientation.

The pivotal partition part may be connected directly to one of the parts of the annulus or rotor, such that rotational movement of the partition part causes angular movement of one of the parts relative to the other without the need for an intervening, and bulky, rack or worm and pinion arrangement.

The indexing means may comprise first and second chambers each of which is provided with a first and second indexing port and a partition which divides the chamber into a first portion including the first indexing port and a second volume including the second indexing port, wherein each partition comprises a part which is pivotally mounted in the chamber for angular movement between a first orientation and a second orientation. In this case, the first and second pivotal partition parts are mounted on a common pivot.

The pivotal part is preferably rotatable between a first position in which the volume of the first portion of the chamber is minimised and the volume of the second portion of the chamber is maximised, and a second position in which the volume of the first portion of the chamber is maximised and the volume of the second portion of the chamber is minimised. In this case, the indexing ports are preferably arranged such that the first indexing port is in communication with the first portion of the chamber and the second indexing port is in communication with the second portion of the chamber when the pivotal part is in either the first position or the second position. This ensures that neither of the indexing ports can be blocked by the pivotal part, when the pivotal part is at the extreme of its travel. This may be achieved by locating each of the ports in a recess in a wall of the chamber. Alternatively, or additionally, this may be achieved by providing the pivotal part with a first and second cut out portion which each provide the pivotal part with an edge which extends around the periphery of the respective indexing port when the pivotal part is in its first or second position respectively.

The partition may further include an angularly fixed part which engages with a bearing portion of the pivotal part so as substantially to prevent leakage of fluid between the first portion and the second portion of the chamber. In this case, indexing means may include biasing means which engages with the angularly fixed part and biases the angularly fixed part into engagement with the bearing portion of the pivotal part.

Preferably, the pump has a single annulus and the rotor being split axially into two parts such that the pump includes two rotors which are relatively angularly adjustable.

In this case, preferably the first rotor is angularly fixed with respect to a drive shaft and the second rotor is movable relative the first rotor. Moreover, the second rotor is preferably mounted on an eccentric mounting part carried by a second shaft which extends along the annulus axis. Thus, the phase of the second rotor relative to the first rotor may be shifted by rotation of the second shaft about the annulus axis.

The pivotal part of the indexing means may be mounted on the second shaft, such that rotation of the pivotal part causes rotation of the shaft and the eccentric on which the second rotor is mounted. Thus, by virtue of this arrangement, the volume occupied by the indexing means is minimised.

The first and second indexing ports are preferably connected to a valve, the valve having a first inlet port which is connected to a source of pressurised fluid and exhaust port which is connected to a low pressure fluid reservoir. The valve may include a valve member which is movable between a first position in which the first indexing port is connected to the exhaust and the second indexing port is connected to a source of pressurised fluid, and a second position in which the first indexing port is connected to a source of pressurised fluid and the second indexing port is connected to the exhaust port. The valve preferably further includes biasing means which biases the valve member into the first position.

The valve member may be configured such that pressurised fluid from the first inlet port acts on the valve member so as to move the valve member from the first position to the second position when the fluid pressure at the first inlet port exceeds a predetermined amount. Alternatively, the valve may include a second inlet port which is connected to a second source of pressurised fluid, pressurised fluid from the second inlet port acting on the valve member so as to move the valve member from the first position to the second position when the fluid pressure at the second inlet port exceeds a predetermined value.

Embodiments of the invention will now be described, by way of example only, with reference to the drawings, of which:

FIG. 1 is an illustration of cross-section through a pump according to the invention;

FIG. 2 is an illustration of a first embodiment of indexing means for the pump illustrated in FIG. 1;

FIG. 3 is a schematic illustration of the indexing means of FIG. 2, along with a valve via which fluid is supplied to the indexing means, the indexing means being in a) a first position and b) a second position;

FIG. 4 is a schematic illustration of an alternative embodiment of indexing means and valve, the indexing means being a) in a first position, and b) in a second position; and

FIG. 5 is a schematic illustration of a further alternative embodiment of indexing means and valve, the indexing means being a) in a first position, and b) in a second position.

Referring now to FIG. 1 there is shown a gerotor pump 10 having an inlet 12 and an outlet 14, and comprising an annulus 16 and first 18 and second 20 male lobed rotors. The annulus 16 is provided with a plurality of internal lobes with which the lobes of the rotors 18, 20 mesh, the rotors 18, 20, in this example, each having one fewer lobe than the annulus 16. It will, of course, be appreciated that the rotors 18, 20 may have more than one fewer lobes than the annulus 16.

The first rotor 18 is mounted fast and centrally on a drive shaft 22 such that the axis of the rotor 18 coincides with the longitudinal axis A of the drive shaft 22, and movement of the rotor 18 with respect to the drive shaft 22 is substantially prevented. The drive shaft 22 is connected to a prime mover, typically an internal combustion engine, but could be driven by an electric motor. In this example, the prime mover is connected to the drive shaft by means of a drive gear 24.

The second rotor 20 is mounted fast on bearing 27, the bearing 27 being rotatably mounted on the eccentric 26, rotation of the second rotor 20 with respect to the eccentric 26 thus being permitted. The eccentric 26 is in turn integral with a second shaft 28, such that the axis B of the second rotor 20 is parallel to but spaced from the longitudinal axis C of the second shaft 28. It will be appreciated, of course, that the eccentric 26 may be mounted fast on the second shaft 28, and these two components need not be integral.

The drive shaft 22 is supported in bearing 32 provided in a pump housing 30 a, and the second shaft 28 is supported in bearing 34 provided in a pump housing cover 30 b. The bearings 32, 34 may each include a seal assembly which substantially prevents fluid from leaking out of the housing 30 around the shaft 22, 28, but the seal assembly may be omitted, particularly if the pump is located in a “wet” environment such as an oil sump.

The housing 30 a and cover 30 b form a housing assembly 30 which surround the annulus 16, and prevents significant translational movement of the annulus 16 whilst permitting rotation of the annulus 16 relative to the housing assembly 30. The axis of rotation of the annulus 16 coincides with longitudinal axis C of the second shaft, and is therefore off-set relative to the axes of rotation A, B of the rotors 18, 20 such that the lobes of the rotors 18, 20 mesh with the internal lobes of the annulus 16.

As will be appreciated from the applicant's previous applications, GB2313411 and EP0565340, as result of the meshing of the lobes of the first rotor 18 with the internal lobes of the annulus 16, rotation of the drive shaft 22 and the first rotor 18 causes the annulus 16 to rotate, which in turn causes the second rotor 20 to rotate as a result of meshing of the lobes of the second rotor 20 with the internal lobes of the annulus 16. Chambers formed between the lobes of the rotors 18, 20 and the annulus 16 change in volume as the annulus 16 and rotors 18, 20 rotate, the chambers increasing in volume in during a first half of the rotation and decreasing in volume during the second half of the rotation.

The pump inlet 12 is positioned in the housing assembly 30 so that it is adjacent to the chambers between the first rotor 18 and the annulus 16 as these increase in volume, so that fluid at the inlet 12 is drawn into the chambers, whilst the pump outlet 14 is positioned in the housing so that it is adjacent to the chambers between the first rotor 18 and the annulus 16 as these decrease in volume, so that fluid in the chambers is ejected through the outlet 14.

As is explained in detail in GB2313411 and EP0565340, when the second shaft is arranged such that the axis B of the second rotor 20 coincides with the axis of rotation of the first rotor 18, as illustrated in FIG. 1, the rotors are in phase, and their lobes are in the same angular relationship to one another. When the pump 10 is operated in this configuration, the flow rate of pumped fluid is maximum for any given speed of rotation of the drive shaft 22. Rotation of the second shaft 28 causes the second rotor 20 to move out of phase with the first rotor 18, so that its axis B is no longer coincident with the axis of rotation A of the first rotor, and the flow rate of pumped fluid at a given speed of rotation of the drive shaft 22 decreases. Thus, the flow rate of pumped fluid can be varied whilst the pump speed remains constant simply by rotation of the second shaft 28. This is known as indexing of the pump 10, and the second rotor 20 is known as the indexing rotor.

In accordance with the present invention, in order to achieve such indexing, the pump 10 is provided with indexing means 36 comprising a chamber 38 having a first indexing port 40 and a second indexing port 42, and a partition 44 which divides the chamber 38 into a first portion 38 a including the first indexing port 40 and a second portion 38 b including the second indexing port 42, the partition 44 comprising a part 46 which is pivotally mounted within the chamber 38 for angular movement relative to the chamber 38 between a first position in which the volume of the first portion 38 a of the chamber 38 is minimised and the volume of the second portion 38 b of the chamber 28 is maximised and a second position in which the volume of the first portion 38 a of the chamber 38 is maximised, and the volume of the second portion 38 b of the chamber 38 is minimised.

A first embodiment of indexing means 36 is illustrated in FIG. 2, and FIGS. 3 a and 3 b. In this embodiment, the chamber 38 is generally wedge shaped and uppermost and lowermost generally parallel walls, and three side walls which extend generally normal to the lowermost and uppermost walls, of which a first side wall 48 a is arcuate, and the second 48 b and third 48 c side walls are generally straight and arranged at an angle of around 120° to one another. The chamber 38 thus forms a sector of a circle subtending an angle of around 120°. The second 48 b and third 48 c side walls do not, however, meet at a point, as a part-cylindrical recess is provided at the intersection of the second and third side walls, the part-cylindrical recess accommodating a pivotally mounted cylindrical pin 50 from which extends a vane 52. The pin 50 and vane 52 extend between the lowermost wall and the uppermost wall of the chamber 38, and from the sidewall in the part cylindrical recess to the first side wall 48 a of the chamber 38, so that together, the pin 50 and vane 52 form the partition 44 which divides the chamber 38 into the first 38 a and second 38 b portions. When the partition 44 is in its first position, as illustrated in FIG. 3 a, the vane 52 engages with the second sidewall 48 b, and when the partition 44 is in its second position, the vane 52 engages with the third sidewall 38 c, as illustrated in FIGS. 2 and 3 b. The pin 50 and vane 52 are fitted sufficiently close to the chamber walls 48 a, 48 b, 48 c so as substantially to prevent flow of fluid between the first 38 a and second 38 b portions of the chamber 38, whilst not being so tightly fitted that rotational movement of the partition 44 within the chamber 38 is prevented.

Two further recesses are provided in the chamber wall in which are located the indexing ports 40, 42. The first indexing port 40 is located in a first recess at the intersection between the first sidewall 48 a and the second sidewall 48 b and the second indexing port 42 is located at the intersection between the first sidewall 48 a and the third sidewall 48 c. It will be appreciated that the location of the indexing ports 40, 42 in such recesses prevents either port from being blocked by the vane 52 when it engages with the second 48 a or third sidewall 48 b when in either the first or second position.

In this example, the pin 50, second shaft 28 and eccentric 26 are integral, the chamber 38 is provided in the housing cover 30 b adjacent the indexing rotor 20, and the pin 50 is provided by an end of the second shaft 28 which extends into the chamber 38. By virtue of this arrangement, the indexing means 36 need not contribute to any significant increase in pump size.

As will be appreciated rotation of the partition 44 within the chamber 38 causes the second shaft 28 to rotate, and the phase of the indexing rotor 20 relative to the first rotor 18 to change. In this example, the pin 50 and vane 52 are arranged such that when the partition 44 is in the first position the indexing rotor 20 is in phase with the first rotor 18, and the flow rate of fluid pumped by the pump 10 at any given drive shaft speed to be maximum. Similarly, when the partition 44 is in the second position, the indexing rotor 20 is around 120° out of phase with the first rotor 18 and the flow rate of fluid pumped by the pump 10 at any given drive shaft speed is at a minimum. It will be appreciated that the angle subtended by the second 38 b and third 38 c sidewalls of the chamber 38 may be varied up to around 180° so as to vary the maximum angular shift of the indexing rotor 20 relative to the first rotor 18, and hence alter the flow rate range of the pump 10. For example, if the second 48 b, and third 48 c sidewalls of the chamber 38 are parallel, movement of the partition 44 to the second position, may bring the indexing rotor 20 180° out of phase with the first rotor 18.

A second embodiment of indexing means 36 is illustrated in FIGS. 4 a and 4 b. In this embodiment, the chamber 38 is disc-shaped, having circular uppermost and lowermost surfaces, and a cylindrical side wall 48 a′, and the partition 44 comprises a fixed vane 54 which extends radially into the chamber 38 from a retaining slot 55 provided in the chamber walls, and bears against a generally semi-circular bearing surface 56 of the pivotal part 46 of the partition 44. The vane 54 is biased into engagement with the bearing portion 56 by means of a helical compression spring 57 which is mounted in the retaining slot 55, such that leakage of fluid between the fixed vane 54 and the bearing portion 56 is substantially prevented. It will be appreciated, of course, that the biasing means need not be a helical compression spring. It may be, for example, a leaf spring or hydraulic fluid may be used to urge the fixed valve 54 into engagement with the bearing portion 56.

The pivotal part 46 of the partition 44 further includes a virtually semicircular barrier portion 58 with substantially the same radius as the chamber 38. The radius of the bearing surface 56 is substantially less than the radius of the barrier portion 58 and the chamber 38, and therefore the pivotal part 46 includes two generally straight edges 60 a, 60 b which, in this example, are generally parallel, and which extend virtually radially between the bearing surface 56 and the outermost semi-circular edge of the barrier portion 58.

The pivotal part 46 is mounted fast on an end of the second shaft 28 which extends into the chamber 38 through an aperture at the centre of the circular lowermost surface of the chamber 38, movement of the pivotal part 46 relative to the second shaft 28 being substantially prevented. The second shaft 28 is positioned such that the distance between the second shaft 28 and the bearing surface 56 is generally constant over the entire extent of the bearing surface 56, and the distance between the second shaft 28 and the outermost semicircular edge of the barrier portion 58 is generally constant over the entire extent of the barrier portion 58. Thus, the outermost edge of the barrier portion 58 bears against the cylindrical sidewall 48 a′ of the chamber 38 to provide a substantially fluid tight seal whilst permitting rotation of the pivotal part 46 relative to the chamber 38.

The pivotal part 46 thus extends from the fixed vane 54 to the cylindrical sidewall 48 a′ of the chamber 38, and both the pivotal part 46 and the fixed vane 54 extend between the lowermost and uppermost chamber walls. The pivotal part 46 and the fixed vane 54 together divide the chamber 38 into first 38 a and second 38 b portions, and substantially prevent flow of fluid between the first 38 a and second 38 b portions. The pivotal part 46 is rotatable through 180° between a first position in which its first straight edge 60 a engages with a first side of the fixed vane 54, as illustrated in FIG. 4 a, a second position in which its second straight edge 60 b engages with a second side of the fixed vane 54 as illustrated in FIG. 4 b. When the pivotal part 46 is in the first position, the volume of the first portion 38 a of the chamber 38 is minimised and the volume of the second portion 38 b of the chamber 38 is maximised. Similarly, when in the pivotal part 46 is in the second position, the volume of the first portion 38 a of the chamber 38 is maximised and the volume of the second portion 38 b of the chamber 38 is minimised.

The indexing ports 40, 42 are provided in the lowermost circular chamber wall, directly adjacent the cylindrical side wall 48 a′, one either side of the fixed vane 54. The pivotal part 46 of the partition 44 include two cut-out portions 62 a,62 b at the intersection between the outmost edge of the barrier portion 58 and the straight edges 60 a, 60 b. The edges of the barrier portion 58 surround the indexing ports 40, 42 so that the barrier portion 58 does not block the first indexing port 40 when the pivotal part 56 is in the first position or the second indexing port 42 when the pivotal part 56 is in the second position.

By virtue of mounting the pivotal part 46 on the second shaft 28, rotation of the partition 44 within the chamber 38 causes the second shaft 28 to rotate, and the phase of the indexing rotor 20 relative to the first rotor 18 to change. In this example, the pin 50 and vane 52 are arranged such that when the partition 44 is in the first position the indexing rotor 20 is in phase with the first rotor 18, and the flow rate of fluid pumped by the pump 10 at any given drive shaft speed to be maximum. Similarly, when the partition 44 is in the second position, the indexing rotor 20 is around 180° out of phase with the first rotor 18 and the flow rate of fluid pumped by the pump 10 at any given drive shaft speed is at a minimum.

It will, of course, be appreciated that the partition 44 may be configured such that the straight edges 60 a, 60 b are not parallel, so as to vary the degree of rotational movement through which the partition 44 can turn, and hence the degree of indexing provided.

In both embodiments of indexing means 36, rotation of the pivotal part 46 of the partition 44 is achieved by the supply of pressurised fluid to the indexing ports 40, 42. The partition 44 is moved from the first position to the second position by the supply of pressurised fluid at the first inlet 40, the pressurised fluid filling the first portion 38 a of the chamber 38 as the volume of the first portion 38 a of the chamber 38 increases. Return of the partition 46 to the first position is achieved by the supply of pressurised fluid at the second inlet 42, the pressurised fluid filling the second portion 38 b of the chamber 38 as the volume of the second portion 38 b of the chamber 38 increases, and allowing the fluid in the first portion 38 a of the chamber 38 to be ejected through the first indexing port 40.

The first and second indexing ports 40, 42 are connected to a valve 64, the valve 64 having a first inlet port 66 which is connected to a source of pressurised fluid and exhaust port 68 which is connected to a low pressure fluid reservoir. The valve 64 may include a valve member 70 which is movable between a first position in which the first indexing port 40 is connected to the exhaust port 68 and the second indexing port 42 is connected to the source of pressurised fluid, and a second position in which the first indexing port 40 is connected to the source of pressurised fluid and the second indexing port 42 is connected to the exhaust port 68. The valve 64 also includes a biasing means, in this example a helical compression spring 72, which biases the valve member 70 into the first position.

A first embodiment of valve 64 is illustrated in FIGS. 3 a and 3 b, and corresponds to the shuttle valve shown and described in EP0565340. The inlet port 66 of this valve is adapted to be connected to either the pump outlet 14, or, where the pump 10 is used to pump lubricant to a main lubricating gallery, or rifle, of an internal combustion engine, to the main lubricating gallery. Thus, when the valve member 70 is in the first position, pressurised fluid from the pump outlet, main gallery or any other suitable point in the lubrication system, is supplied to the second indexing port 42, whilst the first indexing port 40 is connected to the low pressure fluid reservoir, the partition 44 of the indexing means 36 adopts the first position, as illustrated in FIG. 3 a, and the indexing rotor 20 is in phase with the first rotor 18. The flow rate of fluid pumped by the pump 10 is therefore at its maximum for a given drive speed, and will increase as the drive speed increases.

The spring 72 is selected such that the pressurised fluid at the valve inlet 66 can overcome biasing force of the spring 72 and move the valve member 70 from the first position to the second position, as illustrated in FIG. 3 b, when the fluid pressure at the pump outlet 14 or in the main lubricating gallery exceeds a predetermined amount. When the valve member 70 moves to the second position, pressurised fluid from the pump outlet or main gallery is supplied to the first indexing port 40, whilst the second indexing port 42 is connected to the low pressure fluid reservoir, the partition 44 of the indexing means 36 moves to the second position, and the indexing rotor 20 is moved out of phase with the first rotor 18. Thus, when the fluid pressure at the pump outlet or main gallery exceeds a predetermined amount, the flow rate of fluid pumped by the pump 10 decreases.

This decrease in flow rate of pumped fluid will, of course, result in a decrease in fluid pressure at the pump outlet 14 or main gallery, which in turn causes the valve member 70 to return to the first position, and the rotors 18, 20 to be brought back into phase. In practice, therefore, the valve member will oscillate between the first and second positions, and the partition 46 of the indexing means 44 will attain an equilibrium position between its first and second positions. Further increases in drive speed will alter this equilibrium position, driving the rotors 18, 20 further out of phase, and the flow rate of pumped fluid, and pressure at the pump outlet or in the main gallery, will reach a plateau.

A second embodiment of valve 64 is illustrated in FIGS. 4 a and 4 b, and corresponds to the spool valve shown and described in UK application number GB0606210.3. This operates to cap the flow rate of pumped fluid in much the same way as the first embodiment of valve 64, but in this embodiment, the valve inlet 66 is connected to the main gallery, and a second valve inlet 74 is connected to the pump outlet 14. The valve member 70 is configured such that when in its first position, as illustrated in FIG. 4 a, the second indexing port 42 is connected to the pump outlet 14 whilst the first indexing port 40 is connected to the low pressure fluid reservoir via a second exhaust port 68′, and when in its second position, as illustrated in FIG. 4 b, the first indexing port 40 is connected to the pump outlet 14 whilst the second indexing port 42 is connected to the low pressure fluid reservoir via the first exhaust port 68, the valve member 70 being moved from the first position to second position when the fluid pressure in the main gallery is sufficient to overcome the biasing force of the spring 72.

As explained in GB0606210.3, this embodiment of valve member has advantages that the pressure at which the flow rate of pumped fluid plateaus is determined by the fluid pressure in the main gallery, but no fluid is drawn from the main gallery in achieving indexing of the pump 10, and that the fluid pressure available for indexing of the pump 10 is the maximum pressure in the system, i.e. that at the pump outlet.

It should be appreciated that whilst the two embodiments of valve 64 described above are actuated by means of fluid pressure acting against the biasing force of a spring 72, the valves 64 may alternatively be partially or completely electrically actuated. In the case of a partially electrically actuated valve, an electrical solenoid is used to adjust the spring resistance so that the fluid pressure required to move the valve member 70 is altered, whereas in a completely electrically actuated valve, the use of fluid pressure to move the valve member 70 is dispensed with, and movement of the valve member 70 is achieved using an electrical solenoid.

A third embodiment of indexing means is shown in FIGS. 5 a and 5 b, and includes first and second wedge shaped chambers 38, 38′, each of which is provided with a first 40, 40′ and second 42, 42′ indexing port and a partition 44 which divides each chamber into a first portion 38 a, 38 a′ including the first indexing port 40, 40′ and a second portion 38 b, 38 b′ including the second indexing port 42, 42′. Each partition 44 comprises a vane 52, 52′, the vanes 52, 52′ extending diametrically opposite one another from a common pivot 50 which is connected to the second shaft 28 as previously described in relation to the first and second embodiments of indexing means. The vanes 52, 52′ are thus pivotally mounted in the chambers 38, 38′ for angular movement between a first orientation, in which the volume of the first portion 38 a, 38 a′ of the chamber 38, 38′ is minimised and the volume of the second portion 38 b, 38 b′ of the chamber 38, 38′ is maximised (as illustrated in FIG. 5 a), and a second orientation in which the volume of the first portion 38 a, 38 a′ is maximised and the volume of the second portion 38 b, 38 b′ is minimised (as shown in FIG. 5 b).

This embodiment of indexing means is shown in FIGS. 5 a and 5 b as being connected to a valve 64 of the type described above in relation to FIGS. 3 a and 3 b. It will be appreciated, however, that this embodiment of indexing means could equally be connected to the type of valve 64 described above in relation to FIGS. 4 a and 4 b. The first indexing ports 40, 40′ are connected to the valve such that when the valve member 70 is in a first position, the first indexing ports 40, 40′ are connected to the exhaust port 68 and the second indexing ports 42, 42′ are connected to the source of pressurised fluid 66. Fluid pressure at the second indexing ports 42, 42′ thus acts on the vanes 52, 52′ and causes the indexing means to adopt the first position shown in FIG. 5 a. When the valve member 70 is in a second position, the first indexing ports 40, 40′ are connected to the source of pressurised fluid 66 whilst the second indexing ports 42, 42′ are connected to the exhaust port 68. Fluid pressure at the first indexing ports 40, 40′ thus acts on the vanes 52, 52′ and causes the indexing means to adopt the second position shown in FIG. 5 b.

It will be appreciated that, by virtue of providing two vanes 52, 52′ mounted on a common pivot the force available for actuating the indexing means at a given fluid pressure, can be doubled without significantly increasing the size and volume occupied by the indexing means.

The vanes 52, 52′ may be integral with the pivot 50, or may be separate from the pivot 50. In the latter case, preferably the vanes 52, 52′ are formed from a single part mounted in a slot in the pivot 50 so that movement of the vanes 52, 52′ along the length of the slot is permitted. This configuration allows the vanes 52, 52′ to float in the slot, and adjust their position to accommodate any irregularities in the shape of the indexing chambers 38, 38′ and to achieve optimum positioning in the indexing chambers 38, 38′.

When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. 

1. A pump assembly including a gerotor pump having an inlet and an outlet, and comprising an annulus and a lobed rotor, one, but not both, of the rotor or annulus being split axially into two parts, the pump further comprising indexing means for angularly shifting one part relative to the other part, the indexing means comprising a chamber having a first indexing port and a second indexing port, and a partition which divides the chamber into a first portion including the first indexing port and a second portion including the second indexing port, wherein the partition comprises a part which is pivotally mounted within the chamber for angular movement within the chamber.
 2. A pump assembly according to claim 1 wherein the indexing means comprises first and second chambers each of which is provided with a first and second indexing port and a partition which divides the chamber into a first portion including the first indexing port and a second volume including the second indexing port, wherein each partition comprises a part which is pivotally mounted in the chamber for angular movement between a first orientation and a second orientation.
 3. A pump assembly according to claim 2 wherein the first and second pivotal partition parts are mounted on a common pivot.
 4. A pump assembly according to claim 1 wherein the pivotal part is rotatable between a first position in which the volume of the first portion of the chamber is minimised and the volume of the second portion of the chamber is maximised, and a second position in which the volume of the first portion of the chamber is maximised and the volume of the second portion of the chamber is minimised.
 5. A pump assembly according to claim 1 wherein the indexing ports are arranged such that the first indexing port is in communication with the first portion of the chamber and the second indexing port is in communication with the second portion of the chamber when the pivotal part is in either the first position or the second position.
 6. A pump assembly according to claim 5 wherein each of the indexing ports is located in a recess in a wall of the chamber.
 7. A pump assembly according to claim 5 wherein the pivotal part is provided with a first and second cut out portion which each provide the pivotal part with an edge which extends around the periphery of the respective indexing port when the pivotal part is in its first or second position respectively.
 8. A pump assembly according to claim 1 wherein the partition further includes an angularly fixed part which engages with a bearing portion of the pivotal part so as substantially to prevent leakage of fluid between the first portion and the second portion of the chamber.
 9. A pump assembly according to claim 8 wherein the indexing means includes biasing means which engages with the angularly fixed part and biases the angularly fixed part into engagement with the bearing portion of the pivotal part.
 10. A pump assembly according to claim 1 wherein the pump has a single annulus and the rotor being split axially into two parts such that the pump includes two rotors which are relatively angularly adjustable.
 11. A pump assembly according to claim 10 wherein the first rotor is angularly fixed with respect to a drive shaft and the second rotor is movable relative the first rotor.
 12. A pump assembly according to claim 11 wherein the second rotor is mounted on an eccentric mounting part carried by a second shaft which extends along the annulus axis.
 13. A pump assembly according to claim 12 wherein the pivotal part of the indexing means is mounted on the second shaft, such that rotation of the pivotal part causes rotation of the shaft and the eccentric on which the second rotor is mounted.
 14. A pump assembly according to claim 1 wherein the first and second indexing ports are connected to a valve, the valve having a first inlet port which is connected to a source of pressurised fluid and exhaust port which is connected to a low pressure fluid reservoir.
 15. A pump assembly according to claim 1 wherein the valve includes a valve member which is movable between a first position in which the first indexing port is connected to the exhaust and the second indexing port is connected to a source of pressurised fluid, and a second position in which the first indexing port is connected to a source of pressurised fluid and the second indexing port is connected to the exhaust port.
 16. A pump assembly according to claim 15 wherein the valve further includes biasing means which biases the valve member into the first position.
 17. A pump assembly according to claim 16 wherein the valve member is be configured such that pressurised fluid from the first inlet port acts on the valve member so as to move the valve member from the first position to the second position when the fluid pressure at the first inlet port exceeds a predetermined amount.
 19. A pump assembly according to claim 16 wherein the valve includes a second inlet port which is connected to a second source of pressurised fluid, pressurised fluid from the second inlet port acting on the valve member so as to move the valve member from the first position to the second position when the fluid pressure at the second inlet port exceeds a predetermined value. 